You should still be able to use an adjustable reamer, done at a well equipped bike shop,
and carefully clean up the ID of the composite seat tube just until the chosen seat post fits.
you will be cutting away Epoxy rather than steel or aluminum , but a sharp reamer should do the job.( + a cutting fluid )

Took my 27.0 RB1 out to 27.2, since it was my bike, it took about 45 minutes to do carefully.
cutting until the post Just Fit. then stopped cutting.